JP2002093363A - Lamp electrode and high pressure mercury lamp using the electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source that satisfies any of the performance of high efficiency, long life and non-flickering. SOLUTION: This is a lamp electrode E constructed of an electrode head 6 of a large diameter and an electrode axis 7 of a small diameter that protrudes integrally from the electrode head 6. The top end part of the electrode head 6 that is positioned on the other side of the electrode axis 7 is formed in a truncated cone shape that becomes gradually thinner toward the top end, and the top end of the truncated cone 62 is formed in a spherical surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel lamp electrode and a high-pressure mercury lamp using the electrode.

[0002]

2. Description of the Related Art In recent years, as a light source for a projector, a demand for a high-pressure mercury lamp realizing higher efficiency, longer life and flickerlessness has been increasing. In response to this requirement, there is a trade-off relationship between high efficiency, long service life and flickerless, in that if one of the performances is preferentially improved, the other performance will be reduced. A satisfactory high-pressure mercury lamp has not yet been completed.

In order to make a high-pressure mercury lamp highly efficient, the mercury density of the light source is set to 0.2 mg / mm ³ or more, and the luminescent spot temperature of the arc reaches 7500 k. Usually, the mercury density is 0.1mg / mm
^With about ^three light sources, the brightness temperature is about 6000k. Therefore, the thermal burden on the discharge starting point of the high-efficiency high-pressure mercury lamp lamp whose luminance temperature exceeds 7500k (both electrodes in the case of AC and the cathode in the case of DC) is extremely severe. Due to this severe thermal load, the vicinity of the discharge starting point of the electrode is melted, and a lot of tungsten evaporates, and at the same time, the shape deformation near the discharge starting point, for example, the sharpened tip of the electrode is melted and rounded due to surface tension It will cause shape deformation. In addition, much of the evaporated tungsten adheres to the inner surface of the discharge vessel, causing early blackening,
This leads to early light attenuation. This is one cause of the short life of the lamp.

First, regarding the blackening problem, for example, as described above, for the purpose of preventing blackening, it is necessary to enclose a large amount of halogen suitable for transporting tungsten which evaporates in a large amount, but the halogen concentration is 4 ×. As much as 10 ⁻³ μmol / mm ³ . Therefore, at the time of lighting, fluctuation of the arc due to convection in the electrode container is observed, and flicker caused by the fluctuation is confirmed on the screen.

Further, as described above, when the electrode tip is greatly consumed and deformed in shape, and the initially set discharge distance between the opposed electrodes is widened early, the amount of light that can be effectively used in combination with the reflector is extremely reduced. However, as described above, early light amount attenuation may be caused. More specifically, in some types of optical equipment, there is an opening called a LCD panel through which light passes, and an image of the LCD panel is projected on a screen. Therefore, of the light emitted from the light source, only the light effectively used passes through the opening of the LCD panel, and the other light does not pass through the opening of the LCD panel and does not reach the screen. Becomes meaningless. As described above, when the discharge distance increases, the amount of light that does not pass through the opening of the LCD panel increases, and the screen becomes dark.

As for the problem of electrode wear, as shown in FIG. 6, a tungsten coil (2) serving as a heat sink is wound around the tip of a thin electrode rod (26) of an electrode (e).
Measures have been taken to increase 6a) to increase heat capacity and reduce tungsten evaporation. However, in this countermeasure, in the initial stage of the discharge start, the start of the winding or the end of the winding (26b) of the coil having a small edge and having a small mass is particularly observed. This promoted tungsten evaporation of the tungsten coil (26a) in the relevant portion (26b), and the measures taken by coil winding were not definitive as a solution to the blackening problem of the discharge vessel. .

As for other attempts to solve the problem of electrode wear, a method has been employed in which the diameter of only the electrode head (36) is increased and the electrode head (36) is formed in a large-diameter cylindrical shape as shown in FIG. However, since the opposing surface of the electrode head (36) is a plane, the discharge starting point (37) always moves on a large opposing plane (38), which fluctuates in the arc and appears as flickering on the screen, which is also a preferable measure. I couldn't say.

[0008]

SUMMARY OF THE INVENTION The first object of the present invention is to develop a new electrode for a high-pressure mercury lamp which simultaneously satisfies both high efficiency, long life and flickerless performance. The second object of the present invention is to develop a high-pressure mercury lamp which satisfies both high efficiency, long life and flickerless performance by using the electrode.

[0009]

A first aspect of the present invention is a basic form of the electrode (E) for a lamp according to the present invention, wherein (a) a large-diameter electrode head (6) and an electrode head (6). An electrode head (E) for a lamp, comprising an electrode shaft (7) having a small diameter protruded integrally, and (b) an electrode head located on the opposite side of the electrode shaft (7).
(6) is formed in a substantially frusto-conical shape that gradually becomes thinner toward the front end, and the front end of the frusto-conical portion (62) is formed in a spherical surface. "

If the tip of the electrode head (6) is formed in a substantially truncated conical shape, the electrode head (6) can discharge an arc by the truncated cone (62) while maintaining a sufficient mass as a heat sink. The area of the spherical portion (63) at the tip of the truncated cone portion (62) where the starting point (11) is located is reduced, and the starting point (11) is easily limited to the spherical portion (63), so that the arc is stabilized. . In addition, as the shape of the spherical portion (63), for example, when the spherical portion (63) at the tip is a sphere or a part of a spheroid as shown in FIG. In such a case, as shown in FIG. 5, there is a case where the spherical portion protrudes, the base (64) is narrowed, and a part thereof is integrally connected to the truncated cone portion (62). Of course, other cases are also included. Spherical part
Considering the heat transfer of (63), the case of FIGS. 3 and 4 is preferable.

The second aspect of the present invention relates to the frustum portion of the first aspect.
Regarding the taper angle (θ) of 2), it is characterized in that “the taper angle (θ) of the truncated cone portion (62) is 20 ° to 60 °”. When the taper angle (θ) is 20 ° or less, the truncated cone (62)
Becomes too elongated, the tip of the truncated cone portion (62) melts during lighting, and the distance between the electrodes increases. Conversely, the taper angle (θ)
If it is more than 60 °, the truncated cone part (62) is too short,
The arc may fly in (62), causing a problem in the stability of the arc. When the taper angle (θ) is in the above range, the arc is stably generated on the substantially spherical portion (63). By setting the above range, melting and evaporation of the truncated cone portion (62) of the electrode head (6) are suppressed, and a stable lighting state is obtained.

A third aspect of the present invention relates to the relationship between the maximum diameter of the spherical portion and the lamp power according to the first or second aspect, wherein the relationship is 0.0015 ≦ (d1) / (W) ≦ 0.005. And The relationship between the maximum diameter (d1) of the spherical portion (63) and the lamp power (W) is the maximum diameter of the spherical portion (63) with respect to the lamp power (W).
If (d1) is too small, at the time of lighting, the spherical portion (63) melts, the distance between the electrodes increases, the arc becomes unstable, and the amount of evaporation of the electrode constituent material increases, causing blackening. Problems arise. On the other hand, if the maximum diameter (d1) of the spherical portion (63) is too large with respect to the lamp power (W), the starting point (11) of the arc generation is not constant and moves on the spherical portion (63), causing a flicker. become. When “(d1) / (W)” is in the above range, the arc is stable, and the melting and evaporation of the truncated cone portion (62) of the electrode head (6) is suppressed, and a stable lighting state is obtained.

Claim 4 relates to a high-pressure mercury lamp (A1) for AC lighting using the electrode (E) for a lamp (see FIG. 1), wherein sealing portions (3) are provided at both ends of a discharge vessel (2). An envelope (1) having (4) and an electrode head (6) are disposed inside the discharge vessel (2) so as to face each other, and are integrally led out of the electrode head (6) and sealed. Electrode of small diameter embedded in stop (3) (4)
And (7) a high-pressure mercury lamp for AC lighting (A) having the lamp electrode (E) according to any one of claims 1 to 3.
1) wherein the discharge vessel (2) contains 0.2 mg / mm ³ or more of mercury, a required gas, and 1.1 × 10 ⁻⁴ or more and 3.2 × 10 ⁻³ μmol / mm ³
The following halogens are sealed.

When the amount of mercury is 0.152 mg / mm ³ or less, the luminance and color rendering properties are insufficient. By increasing the amount of mercury to more than 0.2 mg / mm ³ , it is possible to secure high luminance and color rendering properties. I can do it.
When such a high amount of mercury is sealed in the discharge vessel (2) in order to obtain high brightness and color rendering, the arc temperature reaches 7500k, and the thermal load on the electrodes (-E) (+ E) is reduced. As a result, the evaporation of the electrode constituent material (tungsten) increases, which adheres to the inner surface of the discharge vessel (2) and causes blackening. The halogen concentration is in the above range.

That is, when the halogen concentration is 1.1 × 10 ⁻⁴ μmol / mm
^In the case of ³ or less, the transport amount of the evaporating substance is too small, so that the normal halogen cycle is hindered, blackening cannot be prevented, and the lamp life is shortened. Conversely, when the halogen concentration is 3.2 × 10 ^-3 μmol / mm ³
In the above case, the electrode (E) is corroded, and in severe cases, the electrode shaft (7) is broken, and the arc fluctuates due to severe convection in the discharge vessel (2),
This will cause flicker during lighting. Then, the magnitude of the fluctuation of the arc increases as the halogen concentration increases. At 3.3 × 10 ⁻⁴ μmol / mm ³ , it was clearly visible on the screen in 500 hours, and at 7 × 10 ⁻³ μmol / mm ³ , it was only 100 hours. This degrades the image on the screen. In addition, as a necessary gas, an argon gas, a xenon gas, or a mixed gas thereof is used as necessary.

Next, regarding the relationship between the mercury amount and the halogen concentration and the electrode head (6), the large diameter portion (61) of the electrode head (6) is used.
Has a sufficient mass to fully function as a heat sink, to withstand the bright spot temperature of up to 7500k due to the high mercury amount, to suppress the evaporation of electrode constituent materials, Since the shape is narrowed down to a substantially truncated cone and the tip is formed in a spherical shape, the arc starting point (11) is easily limited to the spherical portion (63) as described above, and the arc is stabilized. . As a result, it is possible to withstand the above-mentioned severe lighting conditions under a high mercury amount and obtain a long life.

Claim 5 is a further limited version of the high-pressure mercury lamp (A1) for AC lighting according to claim 4, wherein "tube current is I
Amp, the maximum outer diameter of the electrode head (6) is D, the electrode head
(6) When the length is L, 0.75 × I ≦ D × L ≦ 2.9 × I
Is established. "

The “D × L” indicates the size of the electrode head (6). If the size of the electrode head (6) is too large with respect to the tube current with respect to the electrode head (6). Electrode head (6)
If the temperature is too low, the arc extinguishes. If the temperature is too small, the heat capacity is insufficient and the amount of evaporation of the electrode constituent material during lighting increases. When “D × L” is in the above range, the arc does not disappear and the evaporation amount of the electrode constituent material can be suppressed.

Claim 6 relates to a high-pressure mercury lamp (A2) for direct current lighting using the electrode (E) for a lamp, wherein "sealing portions (3) and (4) are provided at both ends of the discharge vessel (2)." An electrode head (6) of an anode (+ E) having a spherical tip at the inside of the envelope (1) and the discharge vessel (2), and the cathode according to any one of claims 1 to 3. The electrode head (6) of (-E) is disposed so as to face the electrode head, and is integrally led out from the electrode heads (6) and embedded in the sealing portions (3) and (4). A high-pressure mercury lamp for direct current lighting (A2) having a lamp electrode (-E) (+ E) composed of an electrode axis (7), and the discharge vessel (2) having a concentration of 0.2 mg / m2.
m ³ and of mercury, and the required gas, 1.1 × 10 ^-4 or more 3.2 × 10
^-3 μmol / mm ³ or less of halogen are enclosed ”.

In this case, the basic configuration is the same as that for the alternating current, except that the shape of the cathode (-E) and the shape of the anode (+ E) and energization conditions are different. Therefore, the amount of mercury, the required gas, the halogen concentration, etc. are the same, and their actions are the same. cathode(-
The lamp electrode (E) according to claims 1 to 3 is used for E), but the anode (+ E) is the arc receiving side because of the claim 1.
Although the lamp electrode (E) described in 3 may be used, it is not necessary to use it separately, and there is no truncated cone portion (62), and the large diameter portion (61) of the electrode head (6) is used. The tip may be spherical. In the present embodiment described later, the latter is used.

In the high-pressure mercury lamp for direct current lighting (A2), since the cathode (-E) and the anode (+ E) have different shapes, the symbols (E) representing the electrodes are (+) (-). The anode is distinguished from the cathode.

Claim 7 is a further limitation of the high-pressure mercury lamp (A2) for direct-current lighting according to claim 6, wherein the tube current is I amperes and the cathode (-E) electrode head (6) is out of the maximum. Diameter D ₁ , cathode (-
The length of the electrode head (6) of E) is L ₁ , and the electrode head of the anode (+ E)
When the maximum outer diameter of (6) is D ₂ and the length of the anode (+ H) electrode head (6) is L ₂ , 0.75 × I ≦ D ₁ × L ₁ ≦ 2.9 × I and 3 ×
A relationship of I ≦ D ₂ × L ₂ ≦ 5 × I is established ”.

The above-mentioned “D ₁ × L ₁ ” and “D ₂ × L ₂ ” indicate the size of the respective electrode heads (6) as described above, and the relationship of the tube current with respect to the electrode heads (6) is also described above. It is as follows. That is, if the size of the electrode head (6) is too large with respect to the tube current, the temperature of the electrode head (6) will be too low and the arc will extinguish.If the size is too small, the heat capacity is insufficient and the electrode at the time of lighting is insufficient. The amount of evaporation of constituent materials increases. "D ₁ ×
When “L ₁ ” and “D ₂ × L ₂ ” are within the above ranges, the arc does not extinguish and the evaporation amount of the electrode constituent material can be suppressed. In the case of direct current, the polarities are distinguished by adding " ₁ " and " ₂ " to "D" and "L".

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to preferred embodiments. FIG. 1 is a diagram showing a high-pressure mercury lamp for alternating current (A1) according to the present embodiment. The envelope (1) is filled with required gases such as argon gas or xenon gas or a mixture of these, mercury, halogen (enclosed in the form of metal halogen, or in the form of mercury halide or methylene bromide). ) Are sealed, and elongated sealing portions (3) (4) protruding from both ends of the discharge vessel (2).

A pair of tungsten electrodes (E) facing each other are arranged in the discharge vessel (2), and the small-diameter electrode shaft (7) of the electrode (E) is connected to one end of a molybdenum foil (8). Welded to. An external lead (9) is welded to the other end of the molybdenum foil (8), and is led out of the sealing portions (3) and (4). The tungsten electrode (E) of the present invention is one obtained by shaving the electrode shaft (7) from a large diameter tungsten rod.
The diameter of (7) is 50% to 30% of the large diameter part (61) of the electrode head (6)
It has become about. The electrodes (E) of the high-pressure mercury lamp for alternating current (A1) are usually given the same numbers because they have the same shape.

The electrode (E) of the high-pressure mercury lamp for alternating current (A1)
3 to 5 are shown in FIGS. Although these are slightly different because of the shape of the spherical portion (63), they are basically large diameter electrode heads.
(6) and a small-diameter electrode shaft (7) integrally projecting from the electrode head (6). The tip portion of the electrode head (6) located on the opposite side of the electrode shaft (7) is formed in a substantially truncated cone shape that gradually becomes thinner toward the tip, and the tip of the truncated cone portion (62) is spherical. Is formed. Frustoconical part
The taper angle (θ) of (62) is such that the taper angle (θ) is 20 ° to 60 °
It is. The slope of the truncated cone portion (62) is not limited to a straight line, and the generatrix may draw a concave curve or a convex curve.

A spherical portion at the tip of the truncated cone portion (62)
The (63) is formed, for example, by cutting the tip of the electrode head (6) into a conical shape, melting the tip of the conical portion (65), and forming the spherical shape by the surface tension. In this case, the shape differs depending on the difference between the taper angle (θ) of the conical portion (65) and the amount of fusion. Fig. 3 shows a spherical part with a small amount of melting at the tip.
(63) is the case like a part of a sphere or spheroid,
FIG. 4 shows a case where the melting amount at the tip is appropriate and hemispherical, and FIG. 5 shows a state where the melting amount at the tip is too large and the spherical portion (63) protrudes. ) Is partly connected to the truncated cone portion (62).
That is, the diameter (d2) of the base (64) <the maximum diameter (d1). Of course, the shape of the spherical portion (63) is not limited to this, and for example, there is a cylindrical portion (not shown) at the base (64) that is integrally connected to the tip of the truncated cone portion (62), and the tip is This includes the case where it is formed on a spherical surface. Needless to say, the shape of the spherical portion (63) need not be a perfect circle, but may have irregularities on the surface.

Between the spherical portion (63) and the lamp power (W), an appropriate value of the spherical portion (63) is determined by "0.0015 ≦ (d1)
/(W)≦0.005 ”has been experimentally derived. More preferably, “0.0025 ≦ (d1) / (W) ≦ 0.0035”. Here, (d1) is the maximum diameter of the spherical portion (63).
The unit of lamp power (W) is watt. Further, a relationship for determining an appropriate size of the electrode head (6) has been experimentally derived between the tube current and the size of the electrode head (6). It has been experimentally confirmed that this relationship is preferably in the range of “0.75 × I ≦ D × L ≦ 2.9 × I” when the maximum outer diameter is D and the length of the electrode head (6) is L. I have.

The amount of mercury sealed in the discharge vessel (2) is:
0.2mg / mm ³ or more, halogen concentration 1.1 × 10 ^-4 or more
3.2 × 10 ⁻³ μmol / mm ³ or less. The halogen concentration is represented by the ion concentration.

Next, the operation at the time of AC lighting will be described. When an AC voltage is applied to the pair of external lead rods (9), an arc is alternately fired between the counter electrodes (E). The arc is the spherical part (63) at the tip of the electrode (E) applied negatively
The arc flies toward the positively applied electrode (E), but the arc generally flies between the closest parts of the spherical portions (63) at the tips of both opposing electrodes (E). The frustoconical portion (62) is formed at the tip of both opposing electrodes (E), so the tip is narrowed and the tip is formed with a spherical portion (63), so the arc is spherical. It is almost limited between the parts (63) and will fly stably. As a result, the arc is stabilized, and flicker is eliminated.

When the arc flies between the spherical portions (63), the electrode bed (6) including the spherical portion (63) is rapidly heated by the heat of the arc, and a mercury amount of 0.2 mg / mm ³ or more is enclosed. Discharge vessel (2)
In this case, the bright spot temperature of the arc reaches 7500k. As a result, the spherical portion (63) close to the arc bright spot (10) is exposed to the high heat and becomes hot, but the heat of the spherical portion (63) has a sufficient mass and acts sufficiently as a heat sink. It is transmitted to the electrode head (6), especially the large diameter part (61), and the spherical part (63)
To suppress the temperature rise. The spherical part (6
In 3), even if the surface is slightly melted during lighting, the original shape is spherical, so that the shape does not change significantly. (For example, if the tip is a triangular pyramid-shaped electrode, the tip is rounded by melting the triangular pyramid and the tip shape changes significantly.) Therefore, the spherical portion (6
Even if the surface of 3) slightly melts, the distance between the electrodes does not change, and stable arc generation is maintained.

Here, when the spherical portion (63) is shaped like a sphere or a part of a spheroid as shown in FIG. 3, or when it is hemispherical or semi-spheroidal as shown in FIG. Heat is smoothly transferred from the spherical part (63) through the truncated cone part (62) to the large diameter part (61), which plays a major role as a heat sink, to avoid overheating of the spherical part (63). Cheap.
On the other hand, as shown in FIG. 5, the spherical portion (63) has a truncated cone portion (62).
It is considered that the probability of the arc jumping to the truncated cone portion (62) of the positive electrode (E) is slightly higher than that in FIG.

On the other hand, in the case of FIG. 5, since the spherical portion (63) protrudes from the truncated cone portion (62), FIG.
The area of the spherical portion (63) where the arc flies is larger than in the case of 4, and the spherical portion (63) protrudes from the truncated cone portion (62). Part (6
3) The spherical part (63)
Arcs become easier to fly between. On the other hand, spherical part
Since the base (64) of (63) is narrowed, the heat transfer to the large-diameter portion (61) is slightly delayed as compared with FIGS. Portion (63) tends to be slightly overheated. In any case, the electrodes of FIGS.
Since the original shape of the spherical portion (63) of (E) is spherical,
The shape does not greatly change, and the change in the distance between the electrodes during lighting is very small.

Next, a high-pressure mercury lamp for direct current (A2) is shown in FIG.
It will be described according to. In order to avoid complication of description, the same parts as those of the high-pressure mercury lamp for alternating current (A1) are denoted by the same reference numerals, and different parts will be mainly described. The different parts are the electrodes (-E) (+ E)
Is different from that of the high-pressure mercury lamp for alternating current (A1) only in that the electron flow continuously flows from the cathode (-E) to the anode (+ E). Other points are high-pressure mercury lamps for AC (A
Same as 1).

The same cathode (-E) as that for AC is used, but while the anode (+ E) is lit, thermoelectrons always collide with the opposing surface (12) of the anode (+ E). To heat the anode (+ E), one having a larger mass than the cathode (-E) is prepared. On the other hand, the cathode (-E)
A high-temperature bright spot (10) appears in the vicinity of the spherical portion (63), and the spherical portion (63) is heated. However, since local heating occurs, a smaller mass than the anode (+ E) is sufficient.

As described above, the shape of the anode (+ E) may be the same as that for AC, but in the case of DC, since it only receives thermoelectrons continuously, the truncated cone portion (62) is Alternatively, the electrode (6a) in which the spherical portion (63) is directly formed at the tip of the large diameter portion (61) may be used. In the case of FIG. 2, the latter electrode head (6a) is employed.

Next, the operation at the time of DC lighting will be described. When a pair of external lead rods (9) are applied, an arc jumps from the anode (-E) to the cathode (+ E). In this case as well, the arc is generally applied to the spherical portion (6) at the tip of both counter electrodes (-E) (+ E).
3) Fly at the closest point between (12). As described above, the tip of the cathode (-E) is formed with a truncated cone (62) and the tip is narrowed, and the tip is formed with a spherical portion (63). The starting point (11) is generated stably in the spherical portion (63), and the movement of the arc is eliminated.

As in the case of the alternating current, the spherical portion (63) was 0.2 mg /
Since an amount of mercury of at least ³ mm3 is enclosed, when an arc is generated on the spherical part (63), the hot spot (10)
The (-E) spherical portion (63) is heated. However, the heat of the spherical portion (63) is transmitted to the electrode head (6) having a sufficient mass and acting sufficiently as a heat sink, particularly the large diameter portion (61), and the temperature rise of the spherical portion (63) is suppressed. You. And the spherical part (63) exposed to high temperature as in the case of AC
During lighting, even if the surface slightly melts, the original shape is spherical, so that the shape does not change significantly.

On the other hand, on the anode (+ E) side, since the opposing tip surface (12) of the electrode head (6a) is formed in a spherical shape, the arc is generally stable toward the top of the opposing tip surface (12). Fly to. Thus, the frusto-conical portion (62) and its opposite end have a spherical portion
The arc is stably generated by the cooperative action of the cathode (+ E) having (63) and the anode (+ E) having the spherical portion (12). Also, the change in the distance between the electrodes during lighting is very small as in the case of AC.

[0040]

As described above, according to the present invention, it is possible to provide a light source which satisfies both high efficiency, long life and flickerless performance. .

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of an AC high-pressure mercury lamp according to the present invention.

FIG. 2 is a sectional view of an embodiment of a high-pressure mercury lamp for direct current according to the present invention.

FIG. 3 is a front view of a first embodiment of an electrode used in the present invention.

FIG. 4 is a front view of a second embodiment of the electrode used in the present invention.

FIG. 5 is a front view of a third embodiment of the electrode used in the present invention.

FIG. 6 is a cross-sectional view of Conventional Example 1.

FIG. 7 is a cross-sectional view of Conventional Example 2.

[Explanation of symbols]

 (E) Lamp electrode (1) Enclosure (2) Discharge vessel (3) (4) Sealing part (6) Electrode head (7) Electrode shaft (61) Large diameter part (62) Truncated cone part (63 ) Spherical part

Claims (7)

[Claims] 1. A lamp electrode comprising a large-diameter electrode head and a small-diameter electrode shaft integrally projecting from the electrode head, wherein a tip of the electrode head located on the opposite side of the electrode axis. An electrode for a lamp, wherein a portion is formed in a substantially truncated cone shape that gradually becomes thinner toward a tip, and the tip of the truncated cone portion is formed in a spherical shape. 2. The taper angle of the truncated cone portion of claim 1 is 20.
An electrode for a lamp, characterized in that the angle is between ° and 60 °. 3. The lamp electrode according to claim 1, wherein the relationship between the maximum diameter of the spherical portion and the lamp power is 0.0015 ≦ d / W ≦ 0.005. 4. An envelope having sealing portions at both ends of a discharge vessel, and an electrode head disposed inside the discharge vessel so as to face each other. A high-pressure mercury lamp for AC lighting, comprising: a lamp electrode according to any one of claims 1 to 3; and a discharge electrode having a diameter of 0.2 mg / mm ^3. A high-pressure mercury lamp for AC lighting, characterized by being filled with the above mercury, necessary gas, and halogen of not less than 1.1 × 10 ^{-4 and not} more than 3.2 × 10 ^-3 μmol / mm ³ . 5. The high-pressure mercury lamp for AC lighting according to claim 4, wherein when a tube current is I amperes, a maximum outer diameter of the electrode head is D, and a length of the electrode head is L, 0.75 × I ≦ D × L. ≤2.9
A high-pressure mercury lamp for alternating current lighting, wherein a relationship of × I is established. 6. The discharge vessel according to any one of claims 1 to 3, wherein the discharge vessel has sealed portions at both ends thereof, and an anode electrode head having a spherical tip formed inside the discharge vessel. DC lighting having a lamp electrode composed of a cathode electrode head and a small-diameter electrode shaft which is integrally led out of the electrode heads and is embedded in a sealing portion. A high-pressure mercury lamp for use, in which the discharge vessel is filled with mercury of 0.2 mg / mm ³ or more, required gas, and halogen of 1.1 × 10 ^{−4 to} 3.2 × 10 ⁻³ μmol / mm ³ or less. High-pressure mercury lamp for direct current lighting characterized by being used. 7. The high-pressure mercury lamp for direct current lighting according to claim 6, wherein the tube current is I amperes and the maximum outer diameter of the cathode electrode head is D.
₁ , when the length of the cathode electrode head is L ₁ , the maximum outer diameter of the anode electrode head is D ₂ , and the length of the anode electrode head is L ₂ , 0.75 × I ≦ D ₁ × L ₁ ≦ 2.9 × I and 3 × I ≦ D ₂ × L
_A high-pressure mercury lamp for direct current lighting, wherein a relationship of ₂ ≦ 5 × I is satisfied.